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BUG: KCSAN: data-race in n_tty_write / tty_set_termios

read-write to 0xffff88810b7ce91c of 4 bytes by task 8162 on cpu 1:
 unset_locked_termios drivers/tty/tty_ioctl.c:254 [inline]
 tty_set_termios+0x1a3/0x870 drivers/tty/tty_ioctl.c:331
 set_termios+0x375/0x3b0 drivers/tty/tty_ioctl.c:414
 tty_mode_ioctl+0x57c/0x680 drivers/tty/tty_ioctl.c:725
 n_tty_ioctl_helper+0x8b/0x460 drivers/tty/tty_ioctl.c:883
 n_tty_ioctl+0x102/0x200 drivers/tty/n_tty.c:2468
 tty_ioctl+0xa9f/0x1030 drivers/tty/tty_io.c:2667
 vfs_ioctl fs/ioctl.c:48 [inline]
 __do_sys_ioctl fs/ioctl.c:753 [inline]
 __se_sys_ioctl+0xcb/0x140 fs/ioctl.c:739
 __x64_sys_ioctl+0x3f/0x50 fs/ioctl.c:739
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

read to 0xffff88810b7ce91c of 4 bytes by task 13166 on cpu 0:
 n_tty_write+0x86/0xae0 drivers/tty/n_tty.c:2312
 do_tty_write drivers/tty/tty_io.c:961 [inline]
 tty_write+0x3f9/0x610 drivers/tty/tty_io.c:1045
 vfs_write+0x21a/0x7c0 fs/read_write.c:603
 ksys_write+0xce/0x180 fs/read_write.c:658
 __do_sys_write fs/read_write.c:670 [inline]
 __se_sys_write fs/read_write.c:667 [inline]
 __x64_sys_write+0x3e/0x50 fs/read_write.c:667
 do_syscall_64+0x39/0x80 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 13166 Comm: syz-executor.2 Not tainted 5.11.0-rc2-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
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